óCoffeeScript Cookbook

A CoffeeScript Type Function


You’d like to know the type of a object without using typeof. (See http://javascript.crockford.com/remedial.html for more information on why typeof is pretty inferior.)


Use the following function:

  type = (obj) ->
    if obj == undefined or obj == null
      return String obj
    classToType = {
      '[object Boolean]': 'boolean',
      '[object Number]': 'number',
      '[object String]': 'string',
      '[object Function]': 'function',
      '[object Array]': 'array',
      '[object Date]': 'date',
      '[object RegExp]': 'regexp',
      '[object Object]': 'object'
    return classToType[Object.prototype.toString.call(obj)]


This function was modeled on jQuery’s $.type function.

Note that, as an alternative to type checking, you can often use duck typing and the existential operator together to eliminating the need to examine an object’s type, in certain cases. For example, here is exception-free code that pushes an element to an array, if myArray is in fact an array (or array-like, with a push function), and does nothing otherwise.

myArray?.push? myValue